Small grains are important cereals for human consumption. However, at present, a significant portion of annual production of small grains is consumed as livestock feed. Small grains contain valuable components such as starch, protein, and dietary fibers. Furthermore, some exemplary small grains, such as barley and oats, contain high amounts (3-8%) of mixed linkage 1-4, 1-3 beta-D-glucan, commonly known as beta-glucan (BG). Because of its unique chemical structure, BG is water-soluble and has become one of the most important dietary fibers for human health. Medical research has shown that BG has hypocholesterolemic effects. Thus in recent years, there is a growing interest in incorporating barley and oats into the human diet since they are naturally healthy, readily available and relatively inexpensive. Unfortunately, unlike wheat and rice, direct consumption of barley and oats as food is typically limited due to lack of certain functionality and palatability.
However, the components of BG, protein, starch, and other fibers in barley and oats have many food uses as well as non-food uses. Thus, there remains a strong and continued industry interest for processing barley and oats into fractions with unique composition. In particular, there is considerable interest in producing fractions enriched in BG, protein, starch, and/or other fibers.
Numerous publications in scientific journals have described various ways to process barley and oats into fractions enriched with BG, protein, starch and/or other fibers. Basically these methods can be grouped into two major categories: dry fractionation and wet extraction. Dry methods include pearling, milling, sieving, air classification or a combination (see e.g., Liu et al. 2009, J. Food Sci. 74:C487-499). Wet methods typically involve solvent extraction, screening or centrifugation, and precipitation.
BG is typically extracted from barley and oats with a solvent and then precipitated by mixing with an alcohol (see e.g., U.S. Pat. No. 5,518,710). Sometimes, certain enzymes (such as amylase and protease) are also used to boost BG recovery (see e.g., U.S. Pat. No. 5,518,710). Wet methods to isolate starch from barley are also available (Andersson et al. 2001, Cereal Chem. 78:507-513). Protein is generally extracted with an alkaline solution and precipitated in acidic conditions (Cluscky et al. 1973, Cereal Chem. 50:475-481).
Compared with wet methods, dry methods are cost effective but suffer with low enrichment levels. Therefore, for production of valuable ingredients with high levels of nutrient enrichment, wet extraction becomes a method of choice. However, almost all reported studies on fractionating barley or oats by wet methods focused on enrichment of either BG or protein and starch. See e.g., U.S. Pat. No. 4,028,468; U.S. Pat. No. 5,013,561; U.S. Pat. No. 5,082,673; U.S. Pat. No. 5,169,660; U.S. Pat. No. 5,183,677; U.S. Pat. No. 5,312,636; U.S. Pat. No. 5,512,287; U.S. Pat. No. 5,518,710; U.S. Pat. No. 5,846,590; U.S. Pat. No. 6,113,908; U.S. Pat. No. 6,197,952; U.S. Pat. No. 6,426,201; U.S. Pat. No. 7,138,519; U.S. Pat. No. 7,566,470. Unfortunately, these methods have limited commercial feasibility due to high cost of recovering only one or two components, leading to low production profitability.
In another development, in recent years, there has been an increase in the demand for ethanol as a fuel additive to decrease the dependency on fossil fuels. This has resulted in a dramatic increase in the demand for starchy grains that can be used for ethanol production. In the U.S. corn is the primary feedstock for fuel ethanol production. In order to avoid the fuel versus food issue, an alternative to corn feedstock is needed. Among others, barley and oats have a great potential as alternative feedstocks for ethanol production.
Unfortunately, ethanol production from barley and oats, is limited by the relatively high content of BG in these grains; The presence of BG not only makes mashes viscous and difficult to handle, but also ends up in the co-product, dried distillers grains with solubles (DDGS), which presents a problem for its use as animal feed. Typically this problem is addressed by adding a BG hydrolyzing enzyme, beta-glucanase, to the production system, so that beta-glucan is converted to glucose. This is reported in a patent application, (see e.g., WO, 2008/1122282). However, the drawback of this approach is that the valuable beta-glucan is not recovered for other uses.
Given the above, what is clearly needed in the art are methods that provide an efficient process for simultaneously enriching BG, protein, starch, and other valuable components from small grains and producing multiple value-added fractions, each enriched with one or more valuable components; methods by which a beta-glucan-enriched fraction can be separated from BG-containing grains (such as barley and oats) before subjecting the rest of biomass to an ethanol production system; and methods for separating proteins out of small grains (such as barley and oats) before subjecting the rest of biomass to an ethanol production process.
Fortunately, as will be clear from the following disclosure, the present invention provides for this and other needs.